I. Field of the Invention
The present invention relates to fuel pumps for aircraft engines and, more particularly, to such pump having two pumping stages.
II. Description of the Prior Art
The previously known fuel pumps for piston aircraft engines typically employ a single stage fuel pump in order to supply fuel to the engine. These fuel pumps, while adequate at low altitude, provide insufficient fuel to the engine at higher altitudes due to high negative inlet pressure as well as vapor formation of the fuel. The high negative inlet pressure reduces the pump's efficiency while the vapor displaces the fuel, both of which contribute to a lower fuel output from the pump.
In order to supply sufficient fuel to the engine at high altitudes, e.g. altitudes in excess of eighteen thousand feet, the previously known aircraft engines have included an electric boost pump which operates in tandem with the standard fuel pump. These electric boost pumps, when activated at high altitudes, supply additional fuel to the engine in order to supply the engine fuel demands.
The previously known electric boost pumps, however, are disadvantageously expensive and also increase the weight of the aircraft. Furthermore, these previously known electric boost pumps suffer from a relatively short life span when operated for prolonged periods of time thus necessitating frequent and expensive maintainance and/or replacement of the boost pump.